1. Field of the Invention
The present invention relates to a penetration detecting apparatus, and particular, the present invention relates to an improvement of a penetration detecting apparatus having a muting function for temporarily suspending the detecting operation of the penetration detecting apparatus.
2. Description of Related Art
Some penetration detecting apparatus detect the penetration of objects toward a forbidden area so as to stop a hazardous apparatus located at the forbidden area, and includes a multi-axis photoelectric penetration detecting apparatus. The multi-axis photoelectric penetration detecting apparatus comprises an emitting unit including a plurality of emitting elements, a receiving unit including a plurality of receiving elements corresponding to the plurality of emitting elements, and a penetration detecting unit for detecting a penetration into the forbidden area based on signals provided from the plurality of the receiving elements. The emitting unit and the receiving unit face each other so that the plurality of emitting elements and the plurality of receiving elements create a plurality of detecting optical axes, namely a light curtain. The penetration detecting unit detects interruption of any one or more detecting optical axes so as to detect the penetration of a person and the like toward the forbidden area.
The emitting units and the receiving units can be disposed on an entrance where objects enter to be processed in a processing machine and can be disposed at the exit as the processed object exits from the processing machine so as to avoid a person accidentally entering into a hazardous area around the processing machine through the entrance or the exit. In this case, however, the processing machine stops at every object to be processed entering or every processed object exiting. Therefore, the multi-axis photoelectric penetration apparatus has a muting function for suspending an object detection temporarily so as to allow the object to be processed through the entrance or the processed object to exit without stopping of the processing machine (referring to Japanese Laid-Open Patent No. 2003-218679). For example, in the case where an object is fed on a conveyer, the muting function is carried out with two additional photoelectric sensors disposed at an upper position on a conveying path than the emitting unit and the receiving unit of the multi-axis photoelectric sensor.
FIG. 9 is a perspective view showing a conveying system including a conventional multi-axis photoelectric penetration detecting apparatus. The conveying system comprises a conveyer V for conveying an object W, and a multi-axes photoelectric penetration detecting apparatus. The multi-axis photoelectric penetration apparatus includes a penetration detecting sensor having an emitting unit 1 and a receiving unit 2 located at an entrance for a processing machine which processes objects W. The objects W are conveyed along a predetermined direction on a conveyer V so as to be processed by the processing machine.
The emitting unit 1 is a light source apparatus including a plurality of emitting elements, such as LED (Light Emitting Diode), and the plurality of emitting elements are arranged in the light source apparatus. The receiving unit 2 is a photoelectric transducer apparatus including a plurality of receiving elements, such as PD (Photo Diode), and the plurality of receiving elements are arranged in the photoelectric transducer apparatus so as to receive light emitted from the plurality of emitting elements respectively. In this case, each of the plurality of emitting elements in the emitting unit 1 is arranged in a line, and each of the plurality of receiving elements in the receiving unit 2 is also arranged in a line.
some penetration sensors include the emitting unit 1 and the receiving unit 2, and are photoelectric sensors including the receiving unit 2 which receives light from the emitting unit 1 directly, namely thru-beam photoelectric sensor. In such a case, at both sides of the conveyer V, the emitting unit 1 and the receiving unit 2 face with each other. The emitting elements and the receiving elements in the photoelectric sensor are arranged on a direction perpendicular to the horizontal plane.
The penetration detecting apparatus can be used to detect a penetration of objects toward a forbidden area to stop an apparatus located at the forbidden area, and can be used to detect the objects passing through an entrance by sensing an interruption of the light, namely a light curtain. In this case, the forbidden area is defined by an area which is located at a lower side of the penetration detecting sensor along the conveying path, and which is surrounded by a protective cage C.
As shown in FIG. 9, sensors A1, A2, B1 and B2 are muting sensors for optically detecting the objects and for providing an outputting signal to the penetration detecting sensor so as to initiate and/or terminate a muting function of the penetration detection. In more detail, the outputting signals of the muting sensors A1 and A2 are provided so that the penetration detecting sensor determines whether the muting function would be activated or not. Thus, the muting sensors A1 and A2 are located at the upper side of the penetration sensor along the conveying path. Moreover, the muting sensor A1 is located more upstream along the conveying path than the muting sensor A2. Therefore, the muting sensor A1 can detect objects W more upstream than the muting sensor A2.
The muting sensors B1 and B2 are located at the lower side of the penetration detecting sensor along the conveying path. In more detail, the muting sensor B1 is located more upstream than the muting sensor B2, and is utilized as a passage sensor for detecting the passage of the objects through the penetration detecting sensor.
In the case where a conveying direction is reversed, the outputting signals of the muting sensors B1 and B2 are provided instead of the outputting signals of the muting sensor A1 and A2 so that the penetration detecting sensor determines whether the muting function would be activated or not. The muting sensor A2 is located at a closer position to the penetration detecting sensor than the muting sensor A1. Thus, the muting sensor A2 is utilized as the passage sensor instead of the muting sensor B2. Each of the muting sensors A1, A2, B1 and B2 comprises an emitting unit for emitting light and a receiving unit for receiving the light from the emitting unit and is a thru-beam photoelectric sensor in which the receiving unit receives the light from the emitting unit directly. The emitting unit and the receiving unit of each of the muting sensors A1, A2, B1 and B2 face with each other and are located at both sides of the conveyer V.
The muting sensors A1, A2, B1 and B2 change an absent detecting status to a present detecting status by detecting a light interruption due to the object W which passes between the emitting unit and the receiving unit of the muting sensor as it travels on the conveyer. The passage of the object W between the emitting unit and the receiving unit of the penetration detecting sensor is detected based on the changing from the present detecting status to the absent detecting status in the muting sensor B1.
The penetration detecting apparatus compares differential time from (a) time at which the photoelectric sensor A1 turns to the present detecting status to (b) time at which the photoelectric sensor A2 turns to the present detecting status with a predetermined time range. When the differential time meets within the predetermined time range, the muting function is initiated. While the muting function is activated, an alarm signal to stop a hazardous apparatus located in the forbidden area, is not activated even if the passage of objects is detected through the penetration detection sensor.
In the above multi-axes photoelectric penetration detecting apparatus, the muting function is not initiated except when the differential time from (a) the time at which the upper muting sensor A1 turns to the present detecting status to (b) the time at which the lower muting sensor A2 turns to the present detecting status, meets within the predetermined time range. In some cases, the muting function is not initiated although the muting function should be initiated. For example, in the case where an object W waits to be processed at a position between the photoelectric sensors A1 and A2 due to a narrow interval between processing machines arranged along a conveying path, the differential time from (a) the time at which the photoelectric sensor A1 turns to the present detecting status to (b) the time at which the photoelectric sensor A2 turns on the present detecting status, does not meet within the predetermined time range. Consequently, the muting function is not initiated.
To solve the above mentioned problem, the muting function may be set to be initiated when both muting sensors A1, A2 turn to the present detecting status in order along the conveying path. In this case, the muting function is initiated regardless of meeting the differential time from within the predetermined time range. In such a case, a target object W and an object without the target object W can be distinguished if a conveying velocity is constant, and, the muting function can be initiated based on the distinction when the target object W is passed. However, the above setting has the following problem. In the case where the photoelectric sensor A1 turns the present detecting status all the time due to a failure of the photoelectric sensor A1 or a shifting position of an optical axis of the photoelectric sensor A1, the muting function is initiated only when the muting sensor A2 turns to the present detecting status.
In general, the muting function is terminated not only when the photoelectric sensor B1 is located at the lower side of a penetration detecting sensor and detects a passage of an object, but also when muting on a continuous time, which is started up from initiating the muting function, in excess of a predetermined period even if the photoelectric sensor B1 does not detect a passage of an object. In some cases, the termination based upon the muting continuation time causes troubles. For example, in the case where conveying of an object W is temporarily suspended so that maintenance of a processing machine can occur, a muting function is likely to be terminated even though maintenance is still occurring on the processing machine. To solve this problem, a penetration detecting sensor having a muting function which is not terminated until the photoelectric sensor B1 detects a passage of an object regardless of a routing continuous time, may be provided. However, although a muting function is initiated only when the photoelectric sensor A2 turns to the present detecting status in the case where the photoelectric sensor A1 continuously provides a signal representing the detection status due to the failure of the photoelectric sensor A1 or accidental shift of an optical axis of the photoelectric sensor A1, the muting function continues to be activated until the photoelectric sensor B1 detects an object.